Bushing well for instrument transformer and transformers including such well

ABSTRACT

Bushing well for use with instrument transformers is molded of a silica filled epoxy material having a conductive ground coating on one end and an opening at the other end to receive the high voltage conductor of the instrument transformer. A conductive coating is provided at such other end to form a high voltage shield for the instrument transformer conductor. The bushing well is molded into the body of a dry-type instrument transformer with the ground coating end adapted to receive a termination module and the conductor of such transformer extending through the opening and into the bushing well.

United States Patent Ouellette et al.

1451 Sept. 30, 1975 1 1 BUSHING WELL FOR INSTRUMENT TRANSFORMER AND TRANSFORMERS INCLUDING SUCH WELL [75] lnventors: Ronald J. Quellette. Derry, NH;

Robert S. Canney, Berwiek, Maine: Ralph B. Stetson. Exeter. NH.

[73] Assignee; General Electric Company,

Schenectady, NY.

[22] Filed: Apr. 8, 1974 [21] Appl. No.: 458,585

[52] US. Cl. 336/84; 174/142; 336/96;

[51] Int. Cl.'- ..H01F 40/00; HOlF 27/04;

H01F 27/36; H01B 17/42 [58] Field of Search 174/11 BH, 18, 73 R. 73 SC, 174/142, 151, 152 R, 167; 336/96, 107, 84; 339/59 R, 60 R, 60 C, 61 R, 94 R, 94 A, 111. 143 R. 143 C [56] References Cited UNlTED STATES PATENTS 2,748,184 5/1956 Nicholas 174/73 SC X Ruete et a1. 339/111 Kotski 339/1 1 1 [57 ABSTRACT Bushing well for use with instrument transformers is molded of a silica filled epoxy material having a conductive ground coating on one end and an opening at the other end to receive the high voltage conductor of the instrument transformer. A conductive coating is provided at such other end to form a high voltage shield for the instrument transformer conductor. The bushing well is molded into the body of a dry-type instrument transformer with the ground coating end adapted to receive a termination module and the conductor of such transformer extending through the opening and into the bushing well.

4 Claims, 4 Drawing Figures U.S. Patent Sept. 30,1975

BUSHING WELL FOR INSTRUMENT TRANSFORMER AND TRANSFORMERS INCLUDING SUCH WELL BACKGROUND OF THE INVENTION This invention relates to instrument transformers and more particularly to a novel bushing well for use with instrument transformers.

In the metering and control field, it is well known to use instrument transformers, such as current transformers and potential transformers to provide isolation from high voltage circuits and to provide a means of transforming high voltagesor currents to values that are convenient for measuring or for use in control circuits. In the usual instrument transformers of the prior art, the high voltage terminal is provided with a blade or othermeans for clamping a high voltage lead to the terminal. See for example, US. Pat. No. 2,997,526. Recently, terminations, orseparable connectors have become available in the distribution field. With these devices now available, it is desirable to provide instrument transformers which-are capable of being used with such separable connectors. However, presently available bushing wells which are used with separable connectors or termination modules,.see U.S. Pat. No. 3,539,972, are not designed for usewith instrument transformers. In particular, those instrument transformers where the exterior is a molded material forming the insulation of the instrument transformer cannot utilize the presently available bushing wells.

It is, therefore,.a particular object of this invention to provide a novel molded bushing wellwhich issuitable for use with dry-type instrument transformers.

A further objectof this invention is to provide a drytype instrument transformer with a molded bushing well molded thereirrfor use with termination modules and separable connectors.

SUMMARYOF THE INVENTION Briefly, in one form, this invention comprises a molded bushing well preferably molded of an epoxy material. The bushing well is cup shaped in form, having a first or outer end portion of one diameter and a second or inner end portion of a larger diameter. A groove is formed on the outer surface between such portions of different diameter. The exterior surface of the first or outer portion is provided with a conductive coating, which extends into the groove, for use as a ground shield. The inner surface of the well is provided with a tapered wall contoured to accept a termination module and has an opening at the base therein for receiving a conductor stud from the high voltage conductor of the instrument transformer. The surface of such opening and the rear portion of the well has a conductive coating for cooperating with the conductor stud to eliminate high voltage stresses in this end of the well.

According to another feature of this invention, the bushing well is molded into the surface of an instrument transformer. The groove is used to secure the bushing well in the instrument transformer and the bushing well provides a means for attaching a termination module to the instrument transformer.

The invention which is sought to be protected will be particularly pointed out and distinctly claimed in the claims appended hereto. However, it is believed that this invention and the manner in which its various objects and advantages are obtained as well as other objects and advantages thereof, will be better understood by referenceto the following detailed description of a preferred embodiment, particularly when considered with the accompanying drawing.

BRIEF DESCRIPTION OF DRAWING FIG. 1 is a perspective view, partially in section, viewed from the front end, of the preferred form of molded bushing well according to this invention;

FIG. 2 is a perspective view, partially in section, similar to FIG. 1 but viewed from the inner end, showing the preferred form of molded bushing well according to the invention;

FIG. 3 is a partial sectional view showing the bushing well of FIGS. 1 and 2 molded in place in an instrument transformer, and;

FIG. 4 is a front elevational view of one form of instrument transformer showing an application of the bushing well of this invention.

DESCRIPTION OF PREFERRED EMBODIMENT In the preferred embodiment of this invention, a molded bushing well is provided for use with dry-type instrument transformers. Referring to the drawing, in which like numerals are used to indicate like parts throughout the various views thereof, and considering first FIGS. 1 and 2, the preferred form of the molded bushing well of this invention will be described. The bushing well 10 is a substantially cup shaped member having a first exterior surface 12 of one diameter and a second exterior surface 14 of a larger diameter. The surface 12, which forms the outer end portion of the bushing 10, and the surface 14, which forms the inner end portion of bushing 10, mate in a groove 16. The groove 16 is used to lock the bushing well 10 into the body of an instrument transformer as will be described more fully hereafter. The bushing well 10 is preferably molded of a silica filled epoxy resin material which provides good dielectric strength and dimensional stability. However, it should be understood that other electrical insulating resinous materials may be used as desired. For example, when the instrument transformer with which the bushing well is to be used is molded of a butyl material, see US. Pat. No. 2,997,526, the well may also be molded of a similar butyl material.

As shown in FIGS. 1 and 2, the surface 12 and end 18 forming the outer portion of the bushing well 10 are coated with a conductive material 20. The conductive material 20 may be a conductive adhesive which will improve the adherence of the material of the bushing well to the insulation of the instrument transformer. The conductive coating 20 will mate with the ground shield of the termination module (not shown) as well as relieving any voltage stress at the interface of the bushing well 10 and the instrument transformer insulation.

The bushing well 10 is provided with an inwardly tapering inner surface or well 22 and has a groove 24 at the bottom or base 26 contoured to receive a termination module. See for example, U.S. Pat. Nos. 3,539,972 and 3,763,461. The base 26 has an opening 28 which is adapted to receive a conductor stud of an instrument transformer. The surface of the opening 28 is provided with a conductive coating 30. The conductive coating 30 will cooperate with the conductor stud of an instrument transformer to provide a high voltage shield to eliminate any high voltage stress at the inner face of opening 28 and the conductor stud, as will be more clearly set out hereafter. In the preferred embodiment shown, a depression 32 is provided in the exterior end of the bushing well for receivinga backup washer. The surface of depression 32 is also provided with a conductive coating 34 which is electrically connected to theconductive coating 30.

FIG. 3 shows the bushing well 10 molded in place in an instrument transformer 40, only a portion of which is shown in FIG. 3. As can be seen from FIG. 3, the bushing 10 is molded into the body 42 of the instrument transformer 40. The insulation 44 of the instrument transformer 40 surrounds almost the entire exterior surface of the bushing well 10 and completely fills the groove 16, firmly locking the bushing well 10 into the body 42 of instrument transformer 40. As clearly appears in FIG. 3, the conductive coating mates with the ground coating 46 of theinstrument transformer 40 and also fills the interface between surface 12 of bushing well 10 and the insulation 44 of the instrument transformer 40, reducing the voltage stresses between such interface. As will be apparent, the conductive coating 20 will also mate with the ground shield on any termination module secured to bushing well 10. A conductor stud 48 having a threaded end 50 extends through opening 28 into bushing well 10. As will be -well understood, conductor stud 48 is connected to the high voltage terminal or lead of instrument transformer 40. As will also be clear, the conductor stud 48 will provide the necessary connection to a termination module secured in bushing well 10. As is shown in FIG. 3,

backup washer.52 is secured in depression 32 and to the conductor stud 48. This backup washer will reduce mechanical stress on the bushing well 10.

FIG. 4' shows a front elevational view of an instrument transformer using the bushing well of this invention. As is shown, bushing wells 10 and 10a are molded into the body 42 of the instrument transformer 40. By means :of bushing wells 10 and 10a, termination modules can bereadily molded in such bushing wells and separable connector elbows can be used to attach high voltage lines to the instrument transformer in a manner well understood by those skilled in the art.

While there has been shown and described the present preferred embodiment of this invention, it will be apparent that modifications may be made without departing from the spirit and scope of the invention, particulary as it is defined in the appended claims.

What is claimed as new and is desired to secure by Letters Patent of the United States is:

l. A molded bushing well for use with instrument transformers to provide high voltage connections thereto comprising: P

a cup shaped body molded of electrical insulating material, said body having a first end portion with an outer surface of one diameter and a second or inner end portion with an'outer surface of a larger diameter, said end portions being joined 'by a groove. said first outer surface having a conductive coating thereon, said cup shaped body having a well therein tapering inwardly from said first end and contoured to receive a termination module, the inner end of said well having an opening for receiving a threaded conductor stud of an instrument transformer, the surface of said opening in said inner end of said well being provided with a conductive coating.

2. A molded bushing well as claimed in claim 1, in which said bushing well is molded of a silica filled epoxy resin. I

3. A molded bushing well as claimed in claim 1, in which said bushing well is molded of a butyl material.

4. An instrument transformer having a body-formed of insulating material and having the bushing well of claim 1 molded therein, the insulating material of said instrument transformer body surrounding substantially the entire outer surfaces of said bushing well and completely filling said groove between said first outer'surface and said second outer surface locking said well into the body of said instrument transformer, and a conductor stud of said instrument transformer extending through said opening and into said we'll. 

1. A molded bushing well for use with instrument transformers to provide high voltage connections thereto comprising: a cup shaped body molded of electrical insulating material, said body having a first end portion with an outer surface of one diameter and a second or inner end portion with an outer surface of a larger diameter, said end portions being joined by a groove, said first outer surface having a conductive coating thereon, said cup shaped body having a well therein tapering inwardly from said first end and contoured to receive a termination module, the inner end of said well having an opening for receiving a threaded conductor stud of an instrument transformer, the surface of said opening in said inner end of said well being provided with a conductive coating.
 2. A molded bushing well as claimed in claim 1, in which said bushing well is molded of a silica filled epoxy resin.
 3. A molded bushing well as claimed in claim 1, in which said bushing well is molded of a butyl material.
 4. An instrument transformer having a body formed of insulating material and having the bushing well of claim 1 molded therein, the insulating material of said instrument transformer body surrounding substantially the entire outer surfaces of said bushing well and completely filling said groove between said first outer surface and said second outer surface locking said well into the body of said instrument transformer, and a cOnductor stud of said instrument transformer extending through said opening and into said well. 